Heart disease is a major cause of morbidity and mortality; care for pediatric and adult heart patients represents a significant portion of the health care dollars spent in this country. Understanding the genetic processes of heart development and function will enhance future treatments for cardiac pathologies. Our work focuses on the Prx2 homeobox gene, a regulatory gene which encodes a DNA binding transcription factor. Prx2 is highly expressed in the embryonic heart, but decreases markedly at birth. The developing limbs and craniofacial mesenchyme also express Prx2. Gene targeting experiments have demonstrated that Prx2 is critical for correct limb and craniofacial morphogenesis as well as normal adult cardiac function. We have recently shown that the Prx2 mutant heart has defined alterations in cardiac contractility and action potential at the organ and cellular level. Thus the Prx2 gene targeted mouse is an excellent model to examine developmental gene regulation that is critical for normal cardiac function. The cardiac deficiencies in the Prx2 mutant may result from altered gene expression established during cardiac development and/or altered expression in the adult heart. Based on our data we hypothesize that Prx2 regulation of collagen expression in the primary mechanism whereby Prx2 is critical for normal cardiac development and function. Specific Aim Number 1 Test the hypothesis that mutations in Prx2 are implicated in human cardiovascular disease. Clone and chromosomally localize the human Prx2 gene to determine if it maps to any regions implicated in cardiovascular disease. Interbreed the Prx2 mutant allele onto different genetic strains of mice. Specific Aim Number 2 Test the hypothesis that collagen expression is regulated by Prx2 in the heart. Determine the pattern and level of collagen expression in the Prx2 mutant heart. Define when in development the Prx2 regulation of collagen begins. Establish and utilize two cell culture systems to examine the Prx2 regulation of collagen in vitro: cardiac fibroblastic cells from the mutant and wild type heart as well as NIH3T3 cells that are stably transfected with sense or antisense constructs of Prx2. Specific Aim Number 3 Evaluate the physiological parameters of altered cardiac function in the Prx2 mutant. Exercise and perform aortic banding of the Prx2 mice to assess cardiac function under stress. Evaluate the beta-adrenergic signalling pathway in the Prx2 mutant heart.